This invention relates to a printing head which is mounted on a portable label printing machine, a desk-type price tag printing machine or the like. More particularly, the invention relates to a printing head which is used for printing bar code characters that are readable from any direction by an optical reading means.
This invention provides a printing head, without an inking device, for printing the bar codes on large-sized labels with required precision. The bar codes are, for example, long and narrow marks arrayed side-by-side and readable from any direction by an optical reading means.
In recent years, computerized POS (point of sales) systems have been adopted in large supermarkets for foods and other household goods. One information indicating means in the POS system is a bar code, the UPC (universal product code) symbol marks which have been developed and established by the American Supermarket Institute. The fundamental consideration in the development of the UPC symbol marks was that the conventional price labels were to be abolished. In this system, the code numbers of markers, kinds of commodities and so forth are represented by the UPC symbol marks. This system was contemplated for source marking, in which the bar codes of UPC symbol marks are applied on the packing boxes and bags when they are produced and thus before they are loaded or filled. Thus, the UPC symbol marks have been printed by large-sized printing machines installed in a packing material factory which make precise and clear prints for optical reading.
Following adoption of the POS system by supermarkets, it has been found that the source marking is insufficient for a complete POS system. Although source marking can be adopted for dry foods, or the like which are produced and/or packaged in food works and certain quantities of which are packed there, the source marking is unsuitable for perishables such as green vegetables and fresh meat. It has thus become necessary to adopt instore marking for commodities to which the bar codes of the UPC symbol marks have not been applied during source marking. For this instore marking, portable label printing machines are used. The UPC symbol marks are printed on labels by the portable printing machines and the printed labels are attached on the surfaces of commodities.
Portable label printing machines are commonly used for printing prices and production dates on labels and for then applying the labels on commodities. The printed information provides purchase information for the customers and information for totalizing the sales by cashiers. When the indicia can be read with the eyes, they are regarded as sufficiently precise.
The UPC symbol marks developed for the purpose of source marking have strict requirements that each character comprise two dark bars and two light spaces, all about 23 mm in length and all arranged in parallel. The breadth of each character is 2.311 mm. with a tolerance of .+-. 0.096 mm.
A rotary printing head, in which types are selected by rotating type rings or stamp belts, are used in the portable label printing machines used in store fronts. But, when the bar code characters of UPC symbol marks are printed on labels by using a conventional portable label printing machine, the preciseness of printed bar code characters is insufficient and optical reading is impossible. When a type ring that has bar code types is axially moved, the breadth of the light spaces are varied and optical reading becomes impossible. Furthermore, in the rotary printing head, there is sideways play, as clearances are formed between the adjoining type rings so as to enable the type rings to rotate easily.
Heretofore, the strict requirements for imprinting UPC symbol marks could not be satisfied using rotary printing heads in the portable label printing machine. THe requirement for precise printing of UPC symbol marks was the most significant obstacle against the adoption of the rotary printing heads.
Further, the conventional rotary printing head is disadvantageous in that the indicating indicia are liable to be stained with ink and are hardly visible as they are small, so that the selection of types becomes troublesome.
In summary, the printing of bar codes of UPC symbol marks by using the conventional portable label printing machine has not been accomplished.